Showing papers on "Thunderstorm published in 1973"

Airflow and Moisture Budget Beneath a Northeast Colorado Hailstorm

Abstract: A case study is presented of a persistent thunderstorm of moderate intensity which occurred in northeast Colorado, and which produced a light hailfall at the ground. The storm was intensively monitored by aircraft, radar, dropsondes, and surface and upper air networks involved in the National Hail Research Experiment. The present study emphasizes the measurements obtained by instrumented aircraft in examining the properties of the subcloud airflow. Large-scale analysis shows that the storm formed on a surface confluence line and subsequently moved toward the region of surface moisture. A brief radar analysis of the storm during the mature stage of its ∼5-hr lifetime is presented, and identifies the general features as belonging to the category termed “supercell” by previous workers. A precipitation analysis is carried out, and rain and hailfall are correlated with the track of the storm. Liberal use of a time-space conversion technique results in detailed mesoscale pressure, temperature, moisture...

The Squall Line Thunderstorm: Numerical Experimentation

Abstract: The structure and mechanism for maintenance of the Great Plains squall line thunderstorm are studied through formulation of a two-dimensional, time-dependent numerical model. The environmental conditions known to be favorable for squall line development and maintenance include a convectively unstable air mass whose motion is characterized by strong vertical shear of the horizontal wind. These conditions are used to specify an environment in an x-z plane upon which a disturbance is superimposed. The appropriate physical equations are integrated forward in time to study changes in the motion, thermal and moisture fields in and around the squall line thunderstorm. The vertical shear of the horizontal environmental wind is varied from one experiment to another with the result that broader and longer lasting cloud circulations occur in the stronger shear cases. Specific areas where three-dimensional effects must be important are discussed from an examination of variable fields during periods when the ...

PICTURE OF THE MONTH: Meso-Highs and Satellite Imagery

Abstract: The meso-High, and how it is produced in an intense thunderstorm area, has been previously explained by Fujita (1963). The passage of the meso-High’s outer boundary is usually accompanied by rain, a vector wind shift, a decrease in surface temperature, and a pressure surge. The intersection of a meso-High boundary with other boundaries (fronts, squall lines, other meso-Highs, mountains, etc.) marks a point with a high potential for intense convective activity.

Electric radiation fields of lightning return strokes in three isolated Florida thunderstorms

Abstract: Peak value and risetime distributions for the electric radiation fields produced by lightning strokes to ground in three isolated Florida thunderstorms are presented. The storm at 195 km produced about 1000 return strokes having an average peak radiation field (normalized to 100 km) of about 5.5 V/m, the storm at 110 km produced about 700 strokes having 2.0 V/m, and the storm within 10 km produced about 100 strokes having 15.0 V/m. For each storm the average peak radiation field for first strokes was only slightly greater than the average peak field for subsequent strokes. For the sample of three storms the average peak radiation field in a given storm was proportional to the number of subsequent strokes per flash in that storm. The field risetimes for the two distant storms have statistical properties which are essentially identical to those reported for distant storms in Pennsylvania, whereas the close Florida storm exhibited significantly faster risetimes.

Twin Tornado Cyclones within a Severe Thunderstorm: Single Doppler Radar Observations

Abstract: (1973). Twin Tornado Cyclones within a Severe Thunderstorm: Single Doppler Radar Observations. Weatherwise: Vol. 26, No. 2, pp. 63-71.

Correlation of Nocturnal Thunderstorms and Boundary-Layer Convergence

Abstract: An analysis is made of 11 Great Plains nocturnal thunderstorm occurrences that have no obvious synoptic scale support. The pressure patterns and local terrain configurations are input to a numerical boundary-layer model that computes the vertically integrated boundary-layer convergence. The time and space phasing of the vertical velocities thus obtained are in good agreement with the time and space phasing of all 11 thunderstorm occurrences for the beginning of the activity, but they are acceptable in only 6 cases for the termination of the activity. There is a tendency for the model to forecast boundary-layer convergence where no thunderstorms occur; but in many such cases, stability and humidity data are unfavorable for thunderstorm activity.

A refinement of the use of K-Values in forecasting thunderstorms in Washington and Oregon

Abstract: Average 1200 GMT K-values and 850-mb temperatures were used to develop an objective aid for making probabi I ity forecasts for afternoon and evening I ightning occurrences in two target areas over Oregon and Washington. Thunderstorm and I ightning reports from airway and Forest Service stations were used in this study. The aid was developed on three summer seasons (1970-72 inclusive). Results on dependent data indicate that the objective forecasts can be expected to be better than climatological probabi I ities for the two target areas, and should be useful in preparing the short-range forecast of probability of thunderstorm occurrence issued during the early morning. Some qualitative synoptic features are discussed for modifying the objective forecast and to localize the concentration of thunderstorm occurrence in the target areas.

Precipitation Characteristics of a Sheared, Moderate Intensity, Supercell-Type Colorado Thunderstorm

Abstract: A dense 450-station network of hail and rain gages in 2025 km2 of northeastern Colorado has provided surface precipitation data from a moderate intensity thunderstorm that crossed the network on 22 July 1972. The storm, which existed in an environmental vertical wind shear of 6 × 10−2 sec−1 for over 4 hr, exhibited characteristics of the supercell-type storm including a well-defined and continuing weak echo region, a deviate motion to the right of the local winds, a precipitation wall advancing toward the region of strongest inflow, and a forward overhang of high reflectivity as far as 10 km and more ahead of the precipitation wall. The surface precipitation network results from the storm are analyzed and correlated with other measurements obtained from precision radar, instrumented aircraft, multiple high-altitude released dropsondes, rawinsondes, and surface observations. Hail recorded at 12 network stations was associated with two inflow regions that existed simultaneously and moved in diverge...

Handbook on Climate of the USSR

Abstract: : The report discusses cloud cover, fog, snowstorms, thunderstorms, and hail as recorded at weather stations in the USSR.

Doppler Radar Observations of the Brookline, Massachusetts Tornado of August

Abstract: A tornado-producing thunderstorm was observed by the AFCRL 5.4-cm pulse Doppler radar in Sudbury, Mass. Quasi-horizontal radial velocity information was used to construct maps depicting the mean air flow within the storm at various altitudes during the occurrence of the tornado.

Sferics and Radar Studies of South Florida Thunderstorms.

Abstract: A Litton Systems 500-kHz, SPARSA/S, 64-channel, thunderstorm-sferics sensor is coupled to the PPI scope of a 10-cm wavelength weather radar. Short vectors protrude from the center of the PPI scope indicating the direction and count rate of sferics discharges. The sferics sensor is thresholded to detect activity within approximately 200 n mi which is equal to the useful range of the weather radar. Thus, the sferics sensor is used to identify thunderstorm precipitation echoes on the radarscope and the combined presentations are photographed on time-lapse 35-mm film. The results of three years of investigations of summer thunderstorms in South Florida are presented. Radar PPI and directional 500-kHz sferics data within 200 n mi of Miami are analyzed for 1967–69. During the years 1968 and 1969, three-dimensional radar data to 100 mi range are also included. Relationships between thunderstorm sferics activity and precipitation echo size, height, intensity, life cycle, and geographical distribution are...

Dropsonde Measurements of Vertical Winds in the Colorado Thunderstorm of 22 July 1972

Abstract: In connection with the National Hail Research Experiment vertical winds were measured in a thunderstorm by 10 special dropsondes dropped side-by-side over a distance of 4 km. The measurements, made at the northern edge of a weak-echo region, showed updrafts up to 13 m sec−1 at middle levels with much variability.

Electrical Balance in the Lower Atmosphere

Abstract: The omnipresent, fluctuating, vertical, negative electric field of fine weather ranges in intensity from 100 or 200 V 1m at the earth's surface to about 5 V 1m at the tropopause. Because the atmosphere is a conductor, this field causes an ionic conduction current to flow of about 10-12 A/m2 or 103 A over the entire globe. This flow of positive charge from the atmosphere to the earth is balanced by various electrical processes that transport positive charge from the earth into the atmosphere at an equal rate. Blowing dust, sand, and snow, volcanic activity and the spray from the ocean play a part, but the primary cause of this atmospheric electrification is the thunderstorm. For reasons that are not understood, large convective clouds produce extensive regions of space charge, electric fields in excess of 105 Vim, and lightning sparks many kilometers in length. Not only the causes, but also the effects of electrification of clouds are still far from being understood. Some scientists believe the electrification is inconsequential, others that it may have important effects, such as accelerating the formation of precipitation.

The electrification of thunderstorms and the formation of precipitation

Abstract: The problem of how thunderstorms become so highly electrified and whether the electricity in thunderstorms has anything to do with the growth of precipitation, especially in some of its unusual forms like hail, has been with science for a long time. Many controversies have developed over the explanation of the electrification. I t now seems probable that the complexity of the questions and the severe difficulties encountered in making scientific measurements within thunderstorms have held up progress in this field. The acquisition of very high-speed high-storage capacity computers and high-resolution fast-response airborne instruments to cope with this complexity has made possible some recent and very significant progress in the understanding of these phenomena. We may conclude now that the bouncing, shattering and breaking of colliding particles in the developing electric field of cumulonimbus clouds will organize the electrical conditions in the cloud to produce the observed characteristics of thunderstorms. An extremely rapid growth rate of the small droplets being formed continuously at cloud base is required in mature thunderstorms to insure that they are not carried through the cloud by the strong updraft without producing the observed heavy precipitation and hail. It has been shown that the electrical conditions inside thunderstorms ,:an act to produce a greatly enhanced growth rate among these very small cloud droplets that otherwise would accrete only extremely slowly.

Ozone and Water Vapor Injected into the Stratosphere from Two Isolated Thunderstorms

Abstract: The local ozone concentration and water vapor overburden were measured from a WB-57F aircraft near thunderstorms that reached or penetrated the tropopause. Two storms were studied extensively: one that penetrated 800 m above the tropopause and another that reached to about the tropopause level. In both cases, water vapor overburdens above and downwind averaged some 40% higher than those upwind of the storms. The water vapor overburdens directly above the higher storm were about 2.4 times that of those background measurements upwind and at the same levels; directly above the weaker storm the water vapor was about 1.8 times as great as the background measurements. The spatial distribution of ozone around the two storms was similar to that of the water vapor: downwind concentrations exceeded those upwind at all levels. An excess in ozone of about 25% was observed in circumnavigations above the storm tops when compared with fair-weather values at the same levels away from the storm. Ozone concentrati...

Ionospheric disturbances due to thunderstorms

Abstract: The paper gives an account of the disturbances in the ionosphere due to the acoustic gravity waves produced by thunderstorms. It explains the phenomena that the ionospheric disturbances in the F-region are numerous and much more pronounced than in the E-region. It describes the mode of travelling of ionospheric disturbances due to horizontally moving waves that escape reflection and travel in the ducting mode. The theoretical analysis tallies fairly well with the experimental work of various authors.

Instrument for Detection of Close Thunderstorms

Abstract: : The article discusses the principles of construction of instruments to detect thunderstorms. The construction and testing of one of the instruments - the thunderstorm signal indicator, is described.

Stationarity in Thunderstorm Rainfall in the Southwest

Abstract: Air -mass thunderstorm rainfall is a major source of water in the rangeland areas of the southwestern United States. These thunderstorms occur during the summer months and produce intense afternoon and evening rains of short duration and limited areal extent. For small (100 square miles and less) watersheds in the southwest, air -mass thunderstorms produce the major flood peaks (Osborn & Hickok, 1968), therefore, knowledge of occurrence frequencies of these thunderstorms is essential in predicting flood sediment transport for small watersheds in the southwest.

Studies of the electrical activity of thunderstorms with lightning flash-counters

Abstract: The results of thunderstorm observations made with local lightning flash counters at Poona during 1967–1969 are presented. A positive correlation between the average total count when the count exceeds 20 per hour on a 5V/m counter, and the number of days per month when thunder is heard has been established. The diurnal and seasonal variations in thunderstorm activity are described. It is seen that although a single isolated storm can vitiate the normal pattern of thunderstorm activity in a month or season, a long term statistical average can be taken with a greater degree of confidence as a better index of electrical activity than the current aural method of observation of thunderstorms.

Characteristics of anvil-top associated with the Poplar Bluff tornado of 7 May 1973

Abstract: Investigation of potential tornado-producing thunderstorms was performed during part of the 1972 and 1973 tornado seasons. On May 7, 1973 twenty-one tornadoes were confirmed over southern Missouri, northern Arkansas, and southwestern Illinois. The region was surveyed by high altitude photography performed on a Learjet over the region of reported tornadoes. Two storms were chosen from aircraft observation with the guidance of ground and radar reports, and a series of photographs were taken of a tornado producing cloud. An analysis of the activity before and during the tornado is made, and most noteworthy were changes detected in the growth and collapse of overshooting domes above the anvil. Suggestions are included for a comprehensive study.